To obtain the best signal-to-noise performance from a wideband VCO generating a microwave signal, it is necessary to lock this signal to a stable source, e.g. a crystal oscillator.
By sampling the output signal from the VCO there is obtained the phase angle of the output signal, which is then fed back so that a constant phase, and thereby a stable signal, is obtained. The technique is generally known and provides certain advantages for the complete microwave generator, e.g. small volume and the facility of generating several frequencies that are multiples of the signal source frequency. A sampling circuit, specially implemented for signals within the microwave range, is used to sample the microwave signal from VCO, and this circuit is the one envisaged by the invention.
A sampling circuit in the prior art for this purpose is described in the IEEE Journal of Solid State Circuits, Vol SC-7, No. 1, February 1972. Typical for this circuit is that it has a complicated mechanical construction, with through plating in the substrate and a plurality of chip components. This known circuit is of the thin film type with bonded-in diodes and capacitors.